1. Field of the Invention
This invention relates to reinforced thermoplastic material and more specifically to apparatus and method for extruding a stampable, reinforced thermoplastic composite sheet containing, as reinforcement, a glass fiber mat.
2. Description of the Prior Art
In the apparatus and method used to form stampable reinforced thermoplastic composite sheets, a long glass fiber mat is sandwiched between a glass fiber filled layer of thermoplastic resin and a fiber-free layer of the resin, and laminated into a multi-ply product while the fiber-free resin layer is in a molten condition.
One of the major problems with such systems is the difficulty of coating substantially all of the fibers of the mat during lamination. The problem is particularly troublesome when mats having a high concentration of glass fiber or utilizing chopped glass fiber strands are employed. In order to alleviate the problem of incomplete coating, it has often been necessary to reduce mat weight and filler concentration, increase resin quantity, utilize resin modifiers and decrease processing speeds. These constraints increase the cost and reduce performance characteristics of the laminated product.